A cooling apparatus for circulating a cooling water in order to cool and/or warm an engine is known heretofore. For example, a Patent Literature 1 discloses a cooling apparatus in which a first cooling water passage which circulates the cooling water and which passes through an inside of the engine and a second cooling water passage which circulates the cooling water and which does not pass through the inside of the engine are connected via a valve. According to the Patent Literature 1, the first cooling water passage is mainly used for cooling and/or warming the engine and second cooling water passage is mainly used for recovering exhaust heat from the engine.
Here, according to the Patent Literature 1, it is determined whether or not there is a closed failure of the valve, which connects the first and second cooling water passages, on the basis of a difference between temperature of the cooling water in the first cooling water passage and temperature of the cooling water in the second cooling water passage. This is because the temperature of the cooling water in the first cooling water passage which passes through the engine has relatively strong tendency to increase more rapidly than the temperature of the cooling water in the second cooling water passage which does not pass through the engine (namely, the difference between both temperatures has relatively strong tendency to increase), when the valve which should be opened is closed.
Incidentally, a Patent Literature 2 is listed as a background art which is related to the present invention.